How can we treat early gastric cancer less invasively and more certainly using endoscopy? What are the criteria to achieve that goal? We conducted this study, taking the following three steps. In the first step, therapeutic outcomes of mucosal resection in patients with early gastric cancer were clinically surveyed over the last decade.As a result, the disappearance rate of tumors was 70% using mucosal resection alone, showing by no means satisfactory outcomes.To analyze the reason, for this, we decided to identify the blind spots in the stomach during mucosal resection, and examined the sizes of specimens that could be obtained in a single resection at different gastric areas occupied by tumors.The results demonstrated that the posterior wall at the upper part of the gastric corpus and the vicinity of the cardiac portion were areas that were difficult to resect. In the second step, considering that development of devices for intragastric manipulation was the most important among conditions necessary for intragastric surgery using a robot, we studied improvements in optical fibers used for laser irradiation.As a result, we developed highly bendable fibers for use in lasers that can also be used for a side-view fiberscope. These fibers allowed laser irradiation at right angles, without any decrease in output. In the third step, clinical outcomes were evaluated again. Additional treatment using the method described above increased the disappearance rate to 100%. The use of this device completed the basic techniques necessary to achieve effective treatment before endoscopic therapy using a robot is introduced.